Comparison of the antimicrobial efficacy of photodynamic therapy with two mediators against Lactobacillus acidophilus in vitro.

Background And Objectives: Lactobacillus is a cariogenic microorganism. Different therapeutic approaches including photodynamic therapy (PDT) have been suggested for treatment of bacterial infection. The purpose of the current study was to compare the effects of PDT with Indocyanine green (ICG) and Methylene blue (MB) photosensitizers (PSs) on Lactobacillus acidophilus (L. acidophilus).

Materials And Methods: In this in-vitro experimental study, 84 samples of L. acidophilus (1 McFarland standard) were compared in 14 experimental groups including: MB, ICG, 660-nm laser, 808-nm laser (pulsed, 74s/continuous-wave, 37s), different combinations of lasers and PSs, Chlorhexidine (CHX) 0.2%, sodium hypochlorite (NaOCl) 2.5%, penicillin 6.3.3 and control groups. The samples were cultured in microplates containing blood agar culture medium. After incubation at 37 °C for 48 h, the colony forming units (CFUs) of L. acidophilus were counted and compared before and after therapeutic interventions. Data were analyzed using SPSS19 software program according to one-way ANOVA test.

Results: This study showed that the separate use of ICG, 660- and 808-nm lasers (pulsed, 74s/continuous-wave, 37s), and the combined use of 808-nm laser (pulsed, 74s/continuous-wave, 37s) and ICG have no significant inhibitory effect on L. acidophilus colonies (P > 0.05), whereas the separate use of MB and the combined use of 660-nm laser (continuous-wave, 37s/pulsed, 74s) and MB significantly inhibited the growth of L. acidophilus in comparison with the control group (p < 0.05). Likewise, CHX 0.2%, NaOCl 2.5% and penicillin 6.3.3 significantly inhibited the bacterial growth (p < 0.05).

Conclusion: The results showed that separate use of MB and combined use of 660-nm laser and MB have a significant inhibitory effect on L. acidophilus growth.